The present invention relates to magnetic scales for position sensors that can be suitably use for position control, position detection, etc. in various devices and particularly suitable for use in bad environment.
Among various examples of the conventionally-known position control techniques is a slide volume control device for a mixer apparatus disclosed in Japanese Patent Publication No. 2748166. In the slide volume control device disclosed in the No. 2748166 patent publication, a slider is supported by two guide rails, and the slider (with a knob and slider terminal attached thereto) is moved by a drive motor. Operational amount (e.g., voltage value) corresponding to a position of the slider is detected by the slider terminal attached to the slider and a resistor unit contacting the slider terminal. Position of the slider is controlled through rotation of the drive motor. Control of a rotational position of such a drive motor depends on a rotational amount of the motor itself.
In such a slide volume control device, it is required that the slider smoothly move and positional control of the slider be accurate and precise both during automatic drive by the motor and during manual drive. Namely, appropriate slide-guiding performance, durability of a slide-guiding structure and accuracy-related durability is required for long-time use. However, because the guide-dedicated structure in the form of the guide rails, the slider-operational-amount detecting structure in the form of the slider terminal and resistor unit and the slider-position controlling structure based on the rotational amount control of the drive motor are separate from one another, the device is complicated in construction and requires high cost.
Further, it is difficult to maintain, for a long time, the accuracy of both of the structure for holding the slider by means of the guide rails and the structure for causing the slide terminal to contact the resistor unit. Furthermore, if a user attempts to maintain the accuracy of both of the structures, clearances between the guide rails and the slider and other requirements tend to become severer, which would make smooth operation of the slider difficult to achieve.
The assignee of the instant application developed a technique for using a magnetic scale and magnetic sensor to directly detect a position of a slider (operator) in a slider volume control device, and the assignee filed a patent application for the developed technique (see Japanese Patent Application Laid-open Publication No. 2006-049302, which corresponds to U.S. patent application Ser. No. 11/333,816 filed on Jan. 17, 2006). According to the developed technique, two parallel movement guide sections are constructed of main and auxiliary movement guides each in the form of a round bar, and a moving block, including an operator and magnetic sensor, is slidably supported on the two movement guide sections. Further, the auxiliary movement guide is constructed as a magnetic scale, and it includes a shaft of a substantial round rod shape, formed by irregular shape drawing of nonmagnetic stainless steel, and a magnetic member embedded in a longitudinal groove formed in the shaft. Position of the moving block is detected by the magnetic sensor detecting the magnetic poles formed in the magnetic member of the auxiliary movement guide. Because the position of the moving block is detected by such a combination of the magnetic scale and magnetic sensor, the detecting accuracy is not lowered even when dust has entered a gap between the magnetic scale and the magnetic sensor; thus, the technique employing the combination of the magnetic scale and magnetic sensor can achieve the advantageous benefit in that it is impervious to dust and dirt.
Also, there have been known printer apparatus where a slider with a print head mounted thereon is moved along a guide shaft. Position of such a print head is controlled by, for example, controlling an amount of movement of a timing belt driving the slider. In this case too, it is desirable that the position of the print head be detectable directly by a magnetic scale and magnetic sensor, because the combination of the magnetic scale and magnetic sensor is impervious to dust and dirt.
Also known today is a technique for controlling a motorcycle or four-wheel vehicle to reduce shaky, jolting movement, etc. of the motorcycle or vehicle by watching an amount of movement of the motorcycle or vehicle. In this case too, it is desirable that the position of the print head be directly detectable by a magnetic scale and magnetic sensor, because the combination of the magnetic scale and magnetic sensor is impervious to dust and dirt.
In the case where the movement guide supporting the movement block is constructed as a magnetic scale, it is conceivable to form the entire movement guide of a permanent magnetic material, such as an alloy or ferrite (type) permanent magnetic material. However, the alloy permanent magnetic material is expensive, and the movement guide formed of the ferrite permanent magnetic material tends to be fragile and have poor durability. If the movement guide is composed mainly of a nonmagnetic stainless steel shaft of a substantial round bar shape as proposed by the assignee of the instant application, the movement guide can advantageously have superior durability. However, with the aforementioned proposed technique, where the movement guide is constructed by embedding the magnetic member in the longitudinal groove formed in the nonmagnetic stainless steel shaft, there is a possibility of part of the magnetic member undesirably peeling off from the shaft. Thus, the conventional technique still has room for improvement in terms of durability.